1. Field of the Invention
The present invention relates to a negative intake pressure detection system in an outboard motor that includes, in an engine compartment defined by an engine hood, an engine, an intake manifold having a plurality of intake branch pipes connected to a plurality of intake ports of the engine, and a throttle body connected to an intake inlet of the intake manifold, wherein the negative intake pressure that is used as a control signal for the engine is detected via the intake manifold.
2. Description of the Prior Art
An outboard motor in which, in order to detect the engine negative intake pressure, a negative pressure detection hole is provided in a pipe wall of an engine intake pipe, one end of a connecting hose is connected to the hole, and the other end of the hose extends and is connected to a negative intake pressure sensor installed in an engine control unit, is known in, for example, Japanese Patent Application Laid-open No. 5-106501.
This conventional negative intake pressure detection system in an outboard motor, since a comparatively long connecting hose is needed, the responsiveness of the negative intake pressure sensor to the change in engine negative intake pressure cannot be said to be good. Furthermore, manipulating a long connecting hose in the cramped engine compartment of an outboard motor undesirably degrades the ease of assembly and maintenance to some extent.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to provide a negative intake pressure detection system in an outboard motor that does not require a connecting hose and can detect the negative intake pressure of an engine with high responsiveness.
In order to achieve the object, in accordance with one aspect of the present invention, a negative intake pressure detection system is provided in an outboard motor that includes, in an engine compartment defined by an engine hood, an engine, an intake manifold including a plurality of intake branch pipes connected to a plurality of intake ports of the engine, and a throttle body connected to an intake inlet of the intake manifold. A negative pressure detection hole that opens within the intake manifold, is provided in the outer wall of the intake manifold, and a negative intake pressure sensor that is fixed to the outer wall, is fitted in the negative pressure detection hole.
In accordance with this arrangement, since the negative intake pressure sensor directly detects the negative intake pressure generated within the intake manifold, the responsiveness of the negative intake pressure sensor to a change in the negative intake pressure of the engine can be enhanced. Moreover, the interior of the intake manifold functions as a surge tank, thereby leveling the intake pulsations of the engine, and as a result the negative intake pressure sensor can detect the negative intake pressure precisely.
Furthermore, since, unlike the prior art arrangement, it is unnecessary to employ a long connecting hose and thus, the ease of assembly and maintenance of the engine can be enhanced.